Since the time of publication of German Pat. No. 725,326, various catalysts have been disclosed for the synthesis of butynediol from formaldehyde and acetylene, known as the Reppe ethynylation reaction. Suitable catalysts have proved to be acetylides of heavy metals, especially copper, which can be obtained from reacting acetylene with the suitable heavy metal compound. In a broader sense, the heavy metal compounds are also described as catalysts because of the fact that the actual catalyst, that is to say the acetylide of the heavy metal, is formed directly on passing acetylene into a suitable reaction mixture which contains the heavy metal compound as a “catalyst precursor” and therefore as a rule the manufacture of the catalyst merely entails manufacturing a suitable heavy metal compound. Accordingly, the use of a particular heavy metal compound of this type is regarded as the actual invention in the text, which follows.
Copper compounds are known to be particularly suitable heavy metal compounds for the above purpose; they include, copper carbonate, copper phosphate, copper formate, copper acetate, copper-(II) chloride, copper-(I) chloride, ammoniacal copper sulfate, copper silicate and copper oxide. These compounds can be used unsupported or may be supported on carriers.
In order to suppress formation of the by-product cuprene during the synthesis of butynediol, additives such as bismuth oxide, bismuth oxyiodide, mercury oxide, mercury iodide, selenium-sulfur, potassium iodide, copper iodide, silver iodide, lead iodide, cerium oxide and selenium dioxide are used (cf. German Pat. No. 740,514 and U.S. Pat. No. 2,300,969).
E. V. Hort (GAF Corporation) U.S. Pat. No. 3,920,759 (1975), discloses a process patent for making butynediol using a copper oxide containing catalyst precursor with about 5 to about 20% copper, 0 to about 3% bismuth, and a magnesium silicate carrier. Importantly, the Hort patent teaches that the catalyst is prepared via impregnation of the magnesium silicate support with a solution of Cu(NO3)2.3H2O and Bi(NO3)3.5H2O.
According to U.S. Pat. No. 3,920,759, the synthesis is carried out with the catalyst, impregnated on an inert powdered carrier, such as magnesium silicate, silica, carbon, alumina and the like, preferably magnesium silicate, at atmospheric pressure with complete safety in as much as any explosive tendency of the overall system is obviated by the inert carrier. The carrier may be prepared in powder form from magnesium silicate having a bulk density of about 0.2 to 1.0 gram/centimeter. A solution of a copper salt, and optionally a bismuth compound are added to the carrier; the bismuth compound inhibits the polymerization of acetylene by copper oxide. The mixture is dried and then calcined to convert the salts to the oxide precursor of the active catalyst.
Currently, BASF markets a Reppe reaction catalyst prepared by the coprecipitation of copper and bismuth nitrates using sodium carbonate, in the presence of a magnesium silicate carrier, in an attempt to coat the carrier particles with the copper and bismuth carbonates and, thus, present a large surface area of copper-containing catalyst. The magnesium silicate is in the form of small spheres with a particle size d50 of about 10 to 20 microns. However, it has been found that when the catalyst is prepared this way, most of the copper and bismuth oxides do not coat the magnesium silicate spheres, and these oxides are present as separate particles not associated with the carrier. While catalysis is maintained, the separate particles are disadvantageous during reaction processing, which involves a filtration step.